Parallel offset calculator
When several conduits are offset together, bending them all at the same marks pinches the rack in the middle of the offset. Shift each following run's marks by the spacing times the tangent of half the bend angle and they stay evenly spaced all the way through.
Parallel offset shift
Run 1 is the conduit on the inside of the first bend. Move both of each next run's marks this much farther from the end.
The parallel offset formula
Shift per run = center-to-center spacing × tan(bend angle ÷ 2)
Run n marks = run 1 marks + (n − 1) × shift
IBEW Local 903's Bending Book states it directly: "multiply the (C-C) measurement of the conduits by the tangent of ½ the bend angle" and advance each succeeding conduit's bends by that figure. Their example: 2″ centers at 30° → 0.2679 × 2″ = 0.536″, about 9/16″.
Worked example: 3 runs at 2″ centers, 30°
- tan(15°) = 0.268. Shift = 2″ × 0.268 = 9/16″.
- Run 1: lay out a normal offset.
- Run 2: both marks 9/16″ farther from the end. Run 3: both marks 1 1/16″ farther.
Shift per inch of spacing
| Angle | tan(θ ÷ 2) | Shift at 2″ centers | Shift at 3″ centers |
|---|---|---|---|
| 10° | 0.087 | 3/16″ | 1/4″ |
| 22½° | 0.199 | 3/8″ | 5/8″ |
| 30° | 0.268 | 9/16″ | 13/16″ |
| 45° | 0.414 | 13/16″ | 1 1/4″ |
| 60° | 0.577 | 1 1/8″ | 1 3/4″ |
Spacing mixed sizes in one rack
When the runs are different sizes, the center-to-center spacing is half of each conduit's outside diameter plus the gap you want between them. With a 1″ gap:
| Pair (EMT) | Center-to-center with 1″ gap |
|---|---|
| 1/2″ + 1/2″ | 1 11/16″ |
| 1/2″ + 3/4″ | 1 13/16″ |
| 3/4″ + 3/4″ | 1 15/16″ |
| 3/4″ + 1″ | 2 1/16″ |
| 1″ + 1″ | 2 3/16″ |
| 1/2″ + 2″ | 2 7/16″ |
| 1-1/4″ + 1-1/4″ | 2 1/2″ |
| 2″ + 2″ | 3 3/16″ |
The BendBoss app does this per pair for every run in the rack — including mixed sizes — and applies the shift automatically.
Common questions
How do you calculate parallel offsets?
Lay out the inside run as a normal offset. Shift each next run's marks by center-to-center spacing × tan(angle ÷ 2), adding one more shift per run.
What is the shift for 30° parallel offsets?
0.268 × the spacing. At 2″ centers that's about 9/16″ per run (IBEW Local 903 Bending Book).
Why not just use the same marks on every conduit?
The outside runs travel farther through the bend. Identical marks pinch the rack together inside the offset.
Does conduit size change the shift?
No. The shift depends only on the spacing and the angle. Size affects the spacing itself — use the outside diameters.
Sources
Every bend on this site, in one app
BendBoss does offsets, saddles, rolling offsets, stub-ups, kicks, parallel runs (mixed sizes), segmented and compound 90s — fraction keypad, bend diagrams and step-by-step walkthroughs. $25.00 once. No subscription, no ads. English and Spanish.
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